1. Refraction and Lenses
(Physics)
Pritam Ghanghas
K. Rohit
Ashok Bishnoi

2. Refraction
Refraction is based on the idea that LIGHT is passing
through one MEDIUM into another it will bend
towards or away the normal and this phenomenon is
called refraction of light. The question is, WHAT
HAPPENS? Suppose you are running on the
beach with a certain velocity when
you suddenly need to run into the
water. What happens to your
velocity?
IT CHANGES!
Refraction Fact #1: As light goes
from one medium to another, the
velocity CHANGES!

3. Refraction
Suppose light comes from air, which in this case will be considered to
be a vacuum, strikes a boundary at some angle of incidence
measured from a normal line ,and goes into water.
The ratio of the two speeds can be compared.
The denominator in this case will ALWAYS
be smaller and produce a unitless value
greater or equal to 1. This value is called the
new medium’s INDEX OF REFRACTION, n.
All substances have an index of refraction and can be used to identify the material.

4. Refraction
Suppose you decide to go spear fishing, but unfortunately you aren’t
having much luck catching any fish.
The cause of this is due to the fact
that light BENDS when it reaches a
new medium. The object is NOT
directly in a straight line path, but
rather it’s image appears that way.
The actual object is on either side of
the image you are viewing.
Refraction Fact #2: As light goes
from one medium to another, the
path CHANGES!

5. Refraction is when light bends as it
passes from one medium into another. normal
When light traveling through air
air
θi
passes into the glass block it is
refracted towards the normal.
glass
block
When light passes back out of the
θr
glass into the air, it is refracted away
from the normal. θi
Since light refracts when it changes
mediums it can be aimed. Lenses are air
shaped so light is aimed at a focal θr
point.
normal

6. The first telescope, designed and built by Galileo, used lenses to focus light from
faraway objects, into Galileo’s eye. His telescope consisted of a concave lens and a
convex lens.
light from convex concave
object lens lens
Light rays are always refracted (bent) towards the thickest part of the lens.

7. Lenses
There are 2 basic types of lenses
A converging lens (Convex) A diverging lens (concave) takes light
takes light rays and bring rays and spreads them outward.
them to a point.

8. •
F
optical axis
Light rays that come in parallel to the optical axis still diverge from the focal point.

9. •
F
optical axis
The first ray comes in parallel to the optical axis and refracts from the focal point.

10. •
F
optical axis
The first ray comes in parallel to the optical axis and refracts from the focal point.
The second ray goes straight through the center of the lens.

11. •
F
optical axis
The first ray comes in parallel to the optical axis and refracts from the focal point.
The second ray goes straight through the center of the lens.
The light rays don’t converge, but the sight lines do.

12. •
F
optical axis
The first ray comes in parallel to the optical axis and refracts from the focal point.
The second ray goes straight through the center of the lens.
The light rays don’t converge, but the sight lines do.
A virtual image forms where the sight lines converge.

13. Convex (Converging) Lens
Much like a mirror, lenses also take light rays from infinity and converge
them to a specific point also called the FOCAL POINT, f. The
difference, however, is that a lens does not have a center of curvature,
C, but rather has a focal point on EACH side of the lens.

14. • • • • •
2F F O F 2F
optical axis
When we put object between O and F,
The image properties will be: -
Virtual errect
Big in size
Behind the mirror

15. When we put object at F,
The image properties will be: -
• • • •
2F F F 2F
optical axis
Real inverted
Very large in size
Meet at infinity

16. When we put object between 2F and F,
The image properties will be: -
• • • •
2F F F 2F
optical axis
Real inverted image
Big in size
Beyond 2F

17. When we put object at 2F,
The image properties will be: -
• • • •
2F F F 2F
optical axis
Real inverted
Same in size
Meet at 2F

18. When we put object beyond 2F,
The image properties will be: -
• • • •
2F F F 2F
optical axis
Real inverted
Small in size
Meet between F and 2F

19. When we object from infinity,
The image properties will be: -
• • • •
2F F F 2F
optical axis
Point size at F
Meet at F
Real inverted

20. When we put object between F and 2F
The image properties will be: -
• •
2F F
optical axis
Virtual erect image
Between 2F and O.
Small in size

21. When we object rays coming from infinity
The image properties will be: -
• •
2F F
optical axis
Virtual erect image
At F.

22. f = focal length
u = object distance
v = image distance
An equation which represents the relation between focal lengh (f) of lens,
object distance (u) and image distance (v) is called lens formula.